1. Field of the Invention
The present invention relates generally to a touch panel, and more particularly, to a method of controlling a noise processing circuit of a touch panel and related noise processing apparatus.
2. Description of the Prior Art
Capacitive touch panels have advantages of the ease of use, which is usually used as interfaces between machine and human. As the capacitive touch panels support multi-touching, and have high transmittance and low power consumption, the capacitive touch panels are widely used in a variety of portable devices, such as smart phones, navigation systems, PDA, and tablet computers.
Please refer to FIG. 1 in conjunction with the following descriptions, which illustrates how a touch panel senses a touch on it. At first, sensing axes X1-Xn of the touch panel 110 are driven each by each, and sensed signals on sensing axes Y1-Yn on the Y-axis with respect to each driven X sensing axis are read out accordingly. Then, the sensing axes Y1-Yn are driven each by each, and sensed signals on sensing axes X1-Xn with respect to each driven sensing Y sensing axis are read out accordingly. In response to the touch, each sensing axis generates the sensed signals with different amounts. With the configuration of a configuration circuit 112 (which could be registers having setting value) inside the sensing circuit 10, the multiplexer 114 sequentially connects the sensing axes to an analog-digital converter (ADC) 116 such that the sensed signals can be read out.
The configuration circuit 112 configures the driving circuit 118 to drive the sensing axes via the multiplexer 114. For example, when the driving circuit 118 drives the sensing axes X1, the configuration circuit 112 configures the multiplexer 114 such that the a sensed signal on a sensing axes Y1 can be accessed. The ADC 116 converts the sensed signal to a digital signal and stored it. Accordingly, the microcontroller 120 loads the digital value. Such operation is repeated until all sensed signals of the sensing axes Y1-Y8 is load by the microcontroller 120. In a consequence, the microcontroller 120 refers to these sensed signals on sensing axes Y1-Y8 to determine whether a touch occurring on the sensing axis X1.
Before the microcontroller 120 refers to the sensed signals to determine whether the touch occurs on the sensing axis X1, a noise processing mechanism is applied to the sensed signal for noise reduction processing. This is because the noise may interfere with the sensing axes of the touch panel 110. Also, each stage of the sensing circuit 10 from the sensing axes to the ADC 116 may be interfered with by the noise, which causes the sensed signal to fail to reflect the touch. Therefore the microcontroller 120 uses noise processing mechanism to remove the noise in the sensed signals. Under the condition that the noise exists, the noise reduction processing can improve the accuracy of touch sensing. However, the noise does not exist, it will significantly increase the workload of the microcontroller 120. Even, the noise reduction processing occupies cycles of the microcontroller 120, which may cause the report rate regarding touch events to be decreased. Also, if the sensed signal without noise is processed with the noise reduction processing, the sensed signal may be distorted.